An arrangement in which a ball (cam follower) is disposed between a helical cam groove formed in an outer peripheral face of a lock pin (lock bolt) that can engage with an engagement recess of a steering shaft and a longitudinal groove formed in an inner peripheral face of a cylindrical rotating body fitted rotatably around the outer periphery of the lock pin, and the lock pin is made to move back and forth by rotating the rotating body back and forth by an electric motor to thus lock and unlock rotation of the steering shaft is known from Patent Document 1 below.
[Patent Document 1] Japanese Patent Application Laid-open No. 2005-343378